The present invention relates to an electronic sewing machine, wherein a predetermined stitch pattern is automatically formed through the use of a needle positioning mechanism and a work feed mechanism controlled by digital information stored in a static memory installed within the electronic sewing machine.
A typical control system of the above-mentioned sewing machine is disclosed in John W. Wurst, U.S. Pat. No. 3,855,956 "SEWING MACHINE STITCH PATTERN GENERATION FROM STITCH DATA STORED IN STATIC MEMORY", patented on Dec. 24, 1974.
In this prior art system, digital information related to the positional coordinates for each stitch of a predetermined stitch pattern is stored in a read only memory (ROM). The digital information stored in the ROM is applied directly to a driving means for controlling movement of stitch forming instrumentality of the sewing machine. Since the ROM output is applied directly to the driving means, the packaging of the ROM-IC should be the socket type to allow the exchange of the ROM when various stitch patterns are desired to be formed. However, this is not favorable in the sewing machine, because oscillation caused by the stitch forming instrumentality will produce ill connection between the ROM and the control circuit assembly.
Moreover, it is desired to modify a portion of the stitch pattern or to enlarge the stitch width when it is required. In the conventional prior art system, the modification of the stitch pattern is not obtainable because the digital information stored in the ROM is applied directly to the driving means associated with the stitch forming instrumentality.